Our objective is to understand the regulation of cell proliferation in the uterus and other organs by all estrogens, natural and synthetic. Until now the actions of estrogens and antiestrogens whether endogenous hormones, drugs, or endocrine disruptors in the environment, have been considered primarily as a 2-component model: the estrogen receptor (ER) and the ligand. This work will analyze responses in terms of 3- components: the ER, the ligand, and the hormone response unit (HRU), which is the estrogen response element (ERE) plus associated factors. The EREs and HRUs of different estrogen responsive genes are different, and our hypothesis is that HRUs could thus selectively regulate gene expression by the ER-ligand complex and by cross talk with other signaling pathways. We will determine (1) if genes with different HRUs are selectively regulated by endogenous and environmental estrogens, (2) if antiestrogens selectively block expression of genes with different HRUs, and (3) if different HRUs are selectively affected by non-ER signaling pathways. The genes to be studied are directly regulated by estrogens and most contain known EREs. In vivo studies of endogenous genes in the rat uterus and a luciferase transgene, + or- an ERE, in transgenic mice will insure that effects occur in a true physiological context. Studies of endogenous genes in M[unreadable][unreadable]-7 human breast cancer cells and transfections with human and rat regulatory sequences will more precisely define the factors responsible for the observed patterns of gene expression, and studies of ER binding to different EREs will indicate how ER-ERE affinity contributes to patterns of gene regulation. In practical terms this proposal asks if different estrogens (e.g., endogenous vs environmental, different endogenous estrogens, etc.) selectively change gene expression, and if different levels of ER occupancy by any single estrogen produce different ratios of hormone regulated gene products. As gene expression is the basis for regulating cell growth and function, the answers are important to understand the reproductive physiology of endogenous estrogens; the pharmacology of answers are important to understand the reproductive physiology of endogenous estrogens; the pharmacology of antiestrogens and drugs used for hormone replacement and contraception; and the toxicity of endocrine disruptors.